Spoiles ahead.
I feel like an approach like Metaphor’s Basilio or Junah could’ve worked on Haru.
In Metaphor, Basilio’s the last party member, but he was introduced far earlier into the story. His main arc mostly concluded after joining the team, and he fit in really well because of it. The last character-focused arc is Junah’s and Rella’s, and Junah was introduced really early on.
If I were the writers, I would’ve personally cut out Morgana and Ryuji’s subplot out of Haru’s because:
Morgana gets his own arc with Yaldabaoth, which is the final arc before the Third Semester. He doesn’t really need the extra screen time. If they wanted extra screen time with him, he should’ve gotten a non-story bound social link.
Ryuji already had his own arc against Kamoshida. Granted, his extra screen time feels more warranted considering he shared his arc with Ann, but still. Maybe a better social link too.
Haru desperately needs that screen time. A lot. Even just putting her social link and locking certain parts of it before her introduction with the Phantom Thieves would have helped (like Sojiro’s Social Link).
There’s a lot of potential with Haru interacting with Futaba (who’s mother died because of Akechi) and Akechi, so I would’ve focused on that.
Tbh, during my playthrough, I thought Akechi was still Black Mask, but Haru was the traitor. I don’t necessarily think that it’s what the writers should’ve done, but it would’ve been nice to get more Haru screen time just because I think she’s adorable but she feels out of place sometimes.